1. Field of the Invention
The invention relates to a controller and a control method for an internal combustion engine.
2. Description of Related Art
A variety of techniques relating to air-fuel ratio learning in internal combustion engines have been disclosed. For example, Japanese Patent Application Publication No. 9-88665 (JP-A-9-88665) describes an internal combustion engine equipped with a controller that executes computational processing for air-fuel ratio learning. The air-fuel ratio learning according to the technique described in JP-A-9-88665 makes it possible to learn a spread in air-fuel ratio caused by a spread occurring during the production of intake air measuring systems such as intake air amount sensors or fuel supply systems such as injectors, or by changes in these systems with time. The results of air-fuel ratio learning are stored as a map in a predetermined storage device, and the air-fuel ratio learning map is referred to, the learning values are retrieved, and the air-fuel ratio learning correction coefficients are set by interpolation in the subsequent control routine performed in the internal combustion engine. The results of air-fuel ratio learning can be reflected in the control of the internal combustion engine by executing such a procedure.
With a configuration in which an air-fuel ratio sensor is mounted on an exhaust passage of an internal combustion engine, the air-fuel ratio of the exhaust gas can be detected with good accuracy from the output signal of the air-fuel ratio sensor, and the output signal of the air-fuel ratio sensor is used for air-fuel ratio learning. However, in the case of a supercharged internal combustion engine having a wastegate valve, the state of the exhaust gas passing through a position where the air-fuel ratio sensor is installed differs between when the wastegate valve is open and when it is closed, and this difference can adversely affect the results of air-fuel ratio learning.